THE COLLOIDAL SOLUTIONS AND THEIR PROPERTIES
A DONNAN EQUILIBRIUM.
The solution - this is a mixture of one or more substances which are dispersed in solvent [e.g. water or another solvent].
The colloidal solution – they are heterogeneous dispersive configuration, in which we can distinguished continues - dispersing phase (solvent) and not continues dispersed phase which particles diameter are 1-100 nm ( 10
-9
– 10
– 7
m), and in case of biopolymers – up to 500 nm.
The properties of colloidal solution:
1. They can be seen in ultra microscope.
2. They do not dialyze.
3. They show Browns motions.
4. They show Tyndall effect.
5. They may coagulate.
Coagulation - it is molecules tendency to create aggregates, which are characteristic for gels
(average above 100nm, 500nm in case of biopolymer), which is characteristic to suspension
[gel]. The opposite phenomena to coagulation is peptization.
These particles loose possibility to remain in solution and they settle down at the bottom of the vessel. This phenomena is called sedimentation.
Coagulation
Sol Gel
Peptization
Classifications of colloidal solutions:
1. Physical state of dispersing and dispersed phase: a) gas dispersed in liquid -microfoam, e.g.: shaving cream, beer foam b) solid dispersed in gas - aerosol, e.g.: smoke, viruses c) liquid dispersed in gas - aerosol ,e.g.: fog. d) liquid dispersed in liquid - emulsion, e.g.: milk, mayonnaise. e) solid dispersed in liquid -sol, e.g.: paint, ink, clay f) gas dispersed in solid - microfoam, e.g.: foam plastics g) liquid dispersed in solid- emulsion, e.g.: butter, cheese, pearl h) solid dispersed in solid, nano-composite, e.g.: injection molded objects
The most common colloids are emulsions and sols which are liquid colloids (dispersing phase is liquid). Sols are solutions of large molecules biopolymers (proteins, sugars, nucleic acids) and sols of metals, sulfur, sulfides, oxides, basics of strong metals.
2. Dimensions of colloidal molecules: a) monodispersive - all three dimensions of molecules are the same. b) multidispersive - the molecules have different dimension (size).
3. The kind of interaction between dispersed and dispersing phase: a/ lyophilic

b/ lyophobic
When solution is water then we called them hydrophilic and hydrophobic.
4. Structure of dispersed phase: a) molecular - most of all mono phase configuration. Their c1assification appears from dimension of molecules. b) micellar - in which the particles of dispersing phase have a small dimensions and small mo1ecu1es mass [soaps, detergents, bile acids]. Its characteristic feature is existence of polarity and inpolarity space within the molecule. c) emulsion - the solutions of nonpolar substances [e.g. lipids] which do not have relationship with dispersing phase [e.g. water].
Characterization of hydrophilic and hydrophobic colloids.
Receiving
Hydrophilic colloids
Dispersion and concentration methods
Hydrophobic colloids
Solution
Stabilization factor
Coagulation
Solvent molecules - e.g. molecules of water (water coat).
Most of all – reversible.
Through subtraction "water coat" after addition great concentration of electrolytes or salts inc1uding polyvalent ions. Also solvents connecting the water may cause hydrophilic colloids coagulation.
Not obvious
Electrolyte ions which is adsorbing from dispersing medium (e.g.mononominal charge)
Most of all- irreversible.
Features of colloid solutions
(such as Brown motion,
TyndalI effect).
Obvious.
The Donnan equilibrium.
The aqua’s surfaces of our organism are separated from each other by semipermeable membranes. It means that some substances can migrate between different aqua’s surfaces, the another can not migrate because of their large dimensions. The influence of not diffused ions on concentration of diffused ions, in two configurations [spaces] separated by semipermeable membrane, is called as Donnan equilibrium.
Let’s think that we have two solutions separated by semipermeable membrane. At first
(before equilibrium state) at the side A we have dissociated sodium salt of protein, and at the side B we have NaCl solution. After establishing of equilibrium, at the side A appears chloride ions and enhance concentration of sodium ions. Protein ion is too big molecule to move through semipermeable membrane and will stay at the side A.

Cellular membrane Cellular membrane
A B A B
Na + Na + Na + Na +
Pr- Cl Pr- Cl -
Cl -
Before equilibrium state established After equilibrium state established
The concentrations of diffusing ions, in state of equilibrium, are not the same at the two sides of membrane. These different concentrations are result of protein ions existence. We may observe the Donnan effect in all biological configurations separated by semipermeable membranes.
EXPERIMENTAL
I.
The Donnan equilibrium .
The protein molecules do not move [not dialyze] through semipermeable membranes, but they affect the movement of other ions. This phenomenon is described as Donnan equilibrium.
Equipment and materials:

4 beakers of volumes 100 cm
3
, glass bar, dialyzing bag filament [thread], universal indicator paper.

Chemicals:
a) 2% albumin solution in 0.9% NaCl
b) concentrated pH indicator

The dialyzing bag should be immersed in distilled water for 15-20 minutes, before the beginning of the experiments.!

Please carefully shake bottle with the indicator before use.

Dilution of pH indicator – take with 5cm
3
glass pipette of concentrated
indicator and pour it into the beaker of 250 cm
3
volume. Fill the beaker with distilled
water to the mark, and shake gently.
Performance:
 pour all the chemicals into the beakers according to the table below:
Chemicals pH indicator – diluted
Beaker 1
Control pH
60 cm
3
Beaker 2
Control pH
60 cm
3
Beaker 3
Dialyzing solution
60 cm
3
Beaker 4
Albumin solution
10ml albumin
- - - 0.4 cm
3 pH indicator – concentrated
HCl 0.1 mol/L
(drop wise) pH
-
7
5-10 drops
(to violet color)
2-3
1-3 drops
(to grey-green color)
3-4
20-30 drops
(to grey-green color)
3-4


The contents of beaker No 4 (albumin solution) should be placed in dialyzing bag.
Close tightly the bag and immerse in beaker No 3 (dialyzing solution).
 Observe the color changes in the bag and dialyzing solution every 15 minutes.
The noticeable change in color will appear after 30 minutes.
II. Receiving hydrophilic colloids (from farina starch and gelatin solutions):

Strew to the bottom of the beaker a little amount of starch and pour a little
amount of distilled water. Let it to bulge (swell). After a few minutes add about
10 cm
3
of distilled water and mix. Heat it, continuously mixing until all starch will dissolve.

Strew to the bottom of beaker a little amount of gelatin and pour a little
amount of distilled water. Let it to bulge (swell). After a few minutes add
about 10 cm 3 of water and shake it. Heat it, continuously mixing, until all starch will dissolve.
III. Analysis of coagulation of hydrophilic colloids of starch and gelatin obtained in experiment II.

Pour into the 2 test tubes about 2 cm
3
of each starch colloidal solution (hydrophilic or hydrophobic).
To one test tube add a little amount (continuously shaking) of solid ammonia
sulfate, until you will see the white precipitate and to the second test tube several drops of acetone until you see changes.
Do the same with gelatin solution.
Write down your observations.